Retinal orientation and interactions in rhodopsin reveal a two-stage trigger mechanism for activation

The 11- cis retinal chromophore is tightly packed within the interior of the visual receptor rhodopsin and isomerizes to the all- trans configuration following absorption of light. The mechanism by which this isomerization event drives the outward rotation of transmembrane helix H6, a hallmark of activated G protein-coupled receptors, is not well established. To address this question, we use solid-state NMR and FTIR spectroscopy to define the...